A computer program stored on a data carrier can be copied any number of times. Manufacturers of commercial computer programs have therefore attempted to protect their products from unauthorized copying or to ensure that unauthorized copies of their computer programs will not run.
Use of a so-called dongle is a special type of copy protection device. A dongle is a hardware module that must be inserted into a module port of a computer in order to use the respective computer program. The program will not run without the dongle. Although the computer program can be copied as often as desired, it can run only on a computer having a dongle inserted in the module port.
However, one disadvantage is that the dongle must always remain inserted into the module port of the computer, usually the serial or parallel port, when using the program. This means that one port of the computer is occupied. Furthermore, the program can no longer be used if the dongle is lost. If several computer programs protected in this way are installed on a computer, the user must change dongles if there are too few available ports.
International Patent Publication No. WO 91/1586 describes a dongle that transfers a data file to the computer on installation of the program and modifies the installed program, which cannot run at first, so that it can be used. Then the dongle is no longer necessary and can be removed. This ensures that the computer program will be used on only one computer. However, then the user does not have the option of installing the program on another computer at a later time because the dongle cannot be reused after a single use.
Therefore, an object of the present invention is to provide a device and a method for preventing bootleg copies of computer programs which will make it possible to use a computer program on different computers at different times.